1. Field of the Invention
The present invention relates to a color separation and color synthesis optical system applied to a reflection type projection display apparatus, and particularly to a color separation and color synthesis optical system capable of suppressing shading occurred for a color image, which is projected onto a screen, due to a difference of thermal expansion coefficients between a wavelength-selective polarization converting plate and a polarization beam splitter, and suppressing a decrease in a contrast ratio owing to an interface reflection light beam of the wavelength selection polarization plate provided on the side where a color-synthesized light beam is emitted.
2. Description of the Related Arts
A projection type display apparatus for projecting a color image is the one which color-separates a white light beam emitted from a light source portion into three primary color light beams of R (red), G (green) and B (blue), guides these three primary color light beams to a spatial light modulators corresponding thereto, and color-synthesizes the three primary color light beams, which have been optically modulated by the spatial light modulators of the three primary colors in accordance with video signals, to project the synthesized color light beam onto a screen, thus allowing the screen to display a color image thereon.
The projection type display apparatus for projecting the color image as described above can be roughly divided into a transmission type projection display apparatus which employs a transmission type spatial light modulator and a reflection type projection display apparatus which employs a reflection type spatial light modulator.
The transmission type projection display apparatus employing the transmission type spatial light modulator can be easily downsized thanks to its relatively simple optical structure. However, the transmission type projection display apparatus has a drawback in its capability for a high resolution performance. On the other hand, though the reflection type projection display apparatus employing the reflection type spatial light modulator has an advantage in its capability for a high resolution performance, this apparatus can not be easily downsized because of its complicated optical structure.
Particularly, the reflection type projection display apparatus employing the reflection type spatial light modulator requires a polarization beam splitter for separating an incident light beam to be radiated onto the reflection type spatial light modulator and a reflected light beam modulated by the reflection type spatial light modulator. At this time, since two or more polarization beam splitters are ordinarily operated for one reflection type spatial light modulator in order to obtain a high contrast color image, this makes the optical structure of the reflection type projection display apparatus complicated.
With respect to such reflection type projection display apparatus employing the reflection type spatial light modulator, a color separation and color synthesis optical system which solves the problem on its optical structure has recently been disclosed with several structural styles by Colorlink Inc. in the United States. For example, refer to the following Non-patent Literature 1, and the following Patent Literature 2.
Non-patent Literature 1: xe2x80x9cHigh Contrast Color Splitting Architecture Using Color Polarization Filtersxe2x80x9d SID 00DIGEST, 92-95(2000), Michael G. Robinson et al.,
Patent Literature 2: U.S. Pat. No. 6,183,091B1
FIG. 1 is a plan view illustrating an optical structure of a color separation and color synthesis optical system applied to a reflection type projection display apparatus that is a conventional example disclosed by Colorlink Inc. FIG. 2 is a plan view illustrating an optical structure of a color separation and color synthesis optical system applied to a reflection type projection display apparatus that is another conventional example disclosed by Colorlink Inc.
The reflection type projection display apparatus 1A that is the conventional example illustrated in FIG. 1 is introduced by Colorlink Inc. in the above described Non-patent Literature 1 (xe2x80x9cHigh Contrast Color Splitting Architecture Using Color Polarization Filtersxe2x80x9d SID 00DIGEST, 92-95(2000), Michael G. Robinson et al.).
The reflection type projection display apparatus, which is the conventional example, constituted of a light source portion 10 for emitting a white light beam; a color separation and color synthesis optical system 30A, which color-separates the white light beam emitted from the light source portion 10 into three primary color light beams of R (red), G (green) and B (blue), guides the three primary color light beams into three spatial light modulators 20R, 20G and 20B corresponding to R, G and B, and emits a color-synthesized light beam obtained by color-synthesizing the three primary color light beams after the three primary color light beams are optically modulated by the spatial light modulators 20R, 20G and 20B depending on video signals; and a projection optical system 40 for projecting the color-synthesized light beam emitted from the color separation and color synthesis optical system 30A.
To be more concrete, the foregoing light source portion 10 is constituted of a reflecting plane mirror 11; a light source 12 using a metal halide lamp, a xenon lamp, a halogen lamp or the like for emitting the white light beam; and a first polarization plate 13 which is provided ahead of the light source 12 and has a transmission axis selected so as to transmit only an s-polarized light beam in the white color light beam therethrough.
Accordingly, when the white light beam from the light source 12 transmits through the first polarization plate 13, Rs, Gs and Bs light beams of three primary colors corresponding to R, G and B are incident onto the color separation and color synthesis optical system 30A provided between the light source portion 10 and the projection optical system 40.
In the following descriptions, the Rs, Gs and Bs light beams of the three primary colors shall show s-polarized light beams respectively corresponding to R, G and B. On the other hand, Rp, Gp and Bp light beams of three primary colors to be described later shall show p-polarized light beams respectively corresponding to R, G and B. At this time, the p and s-polarized light beams are determined based on a relative relation between a plane of polarization of linear polarization and a polarization-splitting plane of a polarization beam splitter onto which the p and s-polarized light beams are incident. When a light beam is in parallel with a paper plane, this light beam is referred to as the p-polarized light beam, and a light beam perpendicular to the p-polarized light beam is referred to as the s-polarized light beam.
The three spatial light modulators 20R, 20G and 20B corresponding to R, G and B use a reflection type liquid crystal panel and the like, and quarter wave plates 21 to 23 are integrally fitted to front planes of the three spatial light modulators (hereinafter, referred to as a reflection type liquid crystal panel) 20R, 20G and 20B. At this time, the quarter wave plates 21 to 23 serve to increase a contrast ratio of images of the respective colors displayed on the reflection type liquid crystal panels 20R, 20G and 20B.
The color separation and color synthesis optical system 30A surrounded by the dotted lines in FIG. 1 is constituted of first to fourth polarization beam splitters 31 to 34 each formed to a rectangular parallelepiped shape (including a regular hexahedron shape), each having approximately the same outside dimension; and first to fourth wavelength-selective polarization converting plates 35 to 38.
Specifically, in the foregoing color separation and color synthesis optical system 30A, first to fourth polarization beam splitters 31 to 34 are located between the light source portion 10 and the projection optical system 40 so as to be separated from each other vertically and horizontally.
In the course of forming each of the first to fourth polarization beam splitters 31 to 34 in such a manner, two triangular prisms formed of optical glass showing no double refraction are jointed to form a rectangular parallelepiped shape, a semi-transmission reflection film which transmits a p-polarized light beam and reflects an s-polarized light beam is formed on one plane of one of the triangular prisms, and another triangular prism is adhered onto the semi-transmission reflection film by use of light transmissivity adhesive, whereby each of polarization separation planes 31a to 34a are formed by the semi-transmission reflection film along a diagonal.
The first to fourth polarization beam splitters 31 to 34 are isolatedly located vertically and horizontally so that the polarization separation planes 31a to 34a intersect to form an approximate X-character shape when viewed from above.
On the right plane side of the second polarization beam splitter 32 located at the top-right position in the drawing, a reflection type liquid crystal panel 20G for G color, to which the quarter wave plate 22 is fitted, is placed so as to face thereto, and, on the left plane side of the third polarization beam splitter 33 located at the bottom-left position in the drawing, a reflection type liquid crystal panel 20B for B color, to which the quarter wave plate 23 is fitted, is placed so as to face thereto. On the lower plane side of the third polarization beam splitter 33, a reflection type liquid crystal panel 20R for R color, to which the quarter wave plate 21 is fitted, is placed so as to face thereto.
Accordingly, in the foregoing color separation and color synthesis optical system 30A, the first polarization beam splitter 31 serves as a member onto which a light beam from the light source portion 10 is incident, and the fourth polarization beam splitter 34 located at the diagonal position to the first polarization beam splitter 31 serves as a member from which a color-synthesized light beam is emitted. The second and third polarization beam splitters 32 and 33 respectively located at the top-right position of the optical system 30A and the bottom-left position of the optical system 30A serve as members for separating incident light beams to be irradiated onto the reflection type liquid crystal panels 20R, 20G and 20B and reflection light beams optically modulated by the reflection type liquid crystal panels 20R, 20G and 20B.
A first wavelength-selective polarization converting plate (phase plate for G color) 35 having a function to rotate the plane of polarization of the G color light beam by 90 degrees is located between the light source portion 10 and the left plane side of the first polarization beam splitter 31. A second wavelength-selective polarization converting plate (phase plate for R color) 36 having a function to rotate the plane of polarization of the R color light beams by 90 degrees is located between the lower plane side of the first polarization beam splitter 31 and the upper plane side of the third polarization beam splitter 33. A third wavelength-selective polarization converting plate (phase plate for the R color) 37 having a function to rotate the plane of polarization of the R color light beam by 90 degrees is located also between the right plane side of the third polarization beam splitter 33 and the left plane side of the fourth polarization beam splitter 34. A fourth wavelength-selective polarization converting plate (phase plate for G color) 38 is also located between the right plane side of the fourth polarization beam splitter 34 and the projection optical system 40.
The foregoing projection optical system 40 is provided at the rear stage of the fourth wavelength-selective polarization converting plate (phase plate for the G color) 38 installed in the color separation and color synthesis optical system 30A, and constituted of a second polarization plate 41 having a transmission axis selected so as to transmit only a linear polarized light beam therethrough, which has a relation of a p-polarized light beam relative to the polarization separation plane 34a of the fourth polarization beam splitter 34; and a projection lens 42 which magnifies and projects a color image light beam.
Herein, an operation of the projection display apparatus 1A having the above described structure, which is the conventional example, will be described.
The white light beam emitted from the light source 12 in the light source portion 10, which is an indefinite polarized light beam, is first incident onto the first polarization plate 13, and only the s-polarized light beam transmits through the first polarization plate 13. Then, the Rs, Gs and Bs light beams of the s-polarized light beam, which correspond to the R, G and B colors, are incident onto the first wavelength-selective polarization converting plate (phase plate for G color) 35 in the color separation and color synthesis optical system 30A.
At this time, as described above, the first wavelength-selective polarization converting plate 35 is the phase plate for the G color, which rotates the plane of polarization only for the G color light beam by 90 degrees. Accordingly, when the Gs light beam of the s-polarized light beam transmits through the first wavelength-selective polarization converting plate 35, the Gs light beam is polarized and converted to the Gp light beam of the p-polarized light beam. Since the first wavelength-selective polarization converting plate (phase plate for G color) 35 does not act on the Rs and Bs light beams of the s-polarized light beam at all, the Rs and Bs light beams transmit intactly through the first wavelength-selective polarization converting plate 35.
Then, the Gp light beam polarized and converted by the first wavelength-selective polarization converting plate (phase plate for the G color) 35 transmits through the polarization separation plane 31a of the first polarization beam splitter 31, and travels straightly to be incident onto the second polarization beam splitter 32. Thereafter, the Gp light beam transmits straightly through the polarization separation plane 32a of the second polarization beam splitter 32, and is incident onto the reflection type liquid crystal panel 20G for the G color, which has the quarter wave plate 22 facing the right side plane of the second polarization beam splitter 32.
Furthermore, in the reflection type liquid crystal panel 20G for the G color, the Gp light beam from the second polarization beam splitter 32 undergoes optical modulation depending on a video signal corresponding to the G color, and becomes the Gs light beam of an s-polarized light beam component generated after being optically modulated. Thus, the Gs light beam is emitted from the reflection type liquid crystal panel 20G.
Thereafter, the Gs light beam from the reflection type liquid crystal panel 20G is sequentially reflected by the polarization separation planes 32a and 34a of the second and fourth polarization beam splitters 32 and 34, and is incident onto the fourth wavelength-selective polarization converting plate (phase plate for G color) 38 located behind the right side plane of the fourth polarization beam splitter 34. Herein, as described above, since the fourth wavelength-selective polarization converting plate 38 is the phase plate for the G color, which has the function to rotate the plane of polarization of the G color light beam by 90 degrees, the Gs light beam of the s-polarized light beam is polarized and converted by the fourth wavelength-selective polarization converting plate 38 to the Gp light of the p-polarized light beam, and emitted to the projection optical system 40 side.
The Rs light beam of the s-polarized light beam, which has transmitted through the first wavelength-selective polarization converting plate (phase plate for G color) 35, is reflected by the polarization separation plane 31a of the first polarization beam splitter 31, and is incident onto the second wavelength-selective polarization converting plate (phase plate for R color) 36 located on the lower plane side of the first polarization beam splitter 31. Herein, since the second wavelength-selective polarization converting plate 36 is the phase plate for the R color, which has the function to rotate the plane of polarization of the R color light beam by 90 degrees, the Rs light beam of the s-polarized light beam is polarized and converted to the Rp light beam of the p-polarized light beam, and incident onto the third polarized light splitter 33 located below the second wavelength-selective polarization converting plate 36.
Thereafter, the Rp light beam straightly transmits through the polarization separation plane 33a of the third polarization beam splitter 33, and is incident onto the reflection type liquid crystal panel 20R for the R color, which has the quarter wave plate 21 facing the bottom side plane of the third polarization beam splitter 33. Moreover, in the reflection type liquid crystal panel 20R for the R color, the Rp light beam from the third polarization beam splitter 33 undergoes optical modulation depending on the video signal corresponding to the R color, and becomes the Rs light beam of the s-polarized light beam component generated after being optically modulated. This Rs light beam is emitted from the reflection type liquid crystal panel 20R.
Thereafter, the Rs light beam from the reflection type liquid crystal panel 20R is reflected by the polarization separation plane 33a of the third polarization beam splitter 33, and is incident onto the third wavelength-selective polarization converting plate (phase plate for the R color) 37 located on the right side plane of the third polarization beam splitter 33. Herein, as described above, since the third wavelength-selective polarization converting plate 37 is the phase plate for the R color, the Rs light beam of the s-polarized light beam is polarized and converted, and incident onto the fourth polarization beam splitter 34.
The Rp light beam of the p-polarized light beam straightly transmits through the polarization separation plane 34a of the fourth polarization beam splitter 34, and is incident onto the fourth wavelength-selective polarization converting plate (phase plate for G color) 38 located at the rear stage of the right side plane of the fourth polarization beam splitter 34. Herein, as described above, since the fourth wavelength-selective polarization converting plate 38 is the phase plate for the G color, the fourth wavelength-selective polarization converting plate 38 does not act on the Rp light beam at all, and the Rp light beam is emitted on the projection optical system 40 side intactly.
The Bs light beam of the s-polarized light beam that has transmitted through the first wavelength-selective polarization converting plate (phase plate for G color) 35 is reflected by the polarization separation plane 31a of the first polarization beam splitter 31, and is incident onto the second wavelength-selective polarization converting plate (phase plate for the R color) 36 located on the lower plane side of the first polarization beam splitter 31. Herein, as described above, since the second wavelength-selective polarization converting plate 36 is the phase plate for the R color, the second wavelength-selective polarization converting plate 36 does not act on the Bs light beam at all, and the Bs light beam is incident onto the third polarization beam splitter 33 intactly.
The Bs light beam is reflected by the polarization separation plane 33a of the third polarization beam splitter 33, and incident onto the reflection type liquid crystal panel 20B for the B color, which has the quarter wave plate 23 facing the left side plane of the third polarization beam splitter 33. Furthermore, in the reflection type liquid crystal panel 20B for the B color, the Bs light beam from the third polarization beam splitter 33 undergoes optical modulation depending on a video signal corresponding to the B color, and becomes the Gp light beam of a p-polarized light beam component generated after being optically modulated. Thus, the Gp light beam is emitted from the reflection type liquid crystal panel 20B.
Thereafter, the Bp light beam from the reflection type liquid crystal panel 20B straightly transmits through the polarization separation plane 33a of the third polarization beam splitter 33, and is incident onto the third wavelength-selective polarization converting plate (phase plate for R color) 37 located on the right side plane of the third polarization beam splitter 33. Herein, as described above, since the third wavelength-selective polarization converting plate 37 is the phase plate for the R color, the third wavelength-selective polarization converting plate 37 does not act on the Bp light beam at all, and the Bp light beam is incident onto the fourth polarization beam splitter 34 intactly.
Furthermore, the Bp light beam straightly transmits through the polarization separation plane 34a of the fourth polarization beam splitter 34, and is incident onto the fourth wavelength-selective polarization converting plate (phase plate for the R color) 38 located at the rear stage of the right side plane of the fourth polarization beam splitter 34. Herein, as described above, since the fourth wavelength-selective polarization converting plate 38 is the phase plate for the G color, the fourth wavelength-selective polarization converting plate 38 does not act on the Bp light beam at all, and the Bp light beam is emitted on the projection optical system 40 side intactly.
Then, the Rp, Gp and Bp light beams are emitted from the fourth wavelength-selective polarization converting plate 38 in a state where their planes of polarization are aligned with the p-polarized light beam, and thereafter a color-synthesized light beam obtained by color-synthesizing the Rp, Gp and Bp light beams transmits sequentially through the second polarization plate 41 and the projection lens 42 in the projection optical system 40. Thus, the color-synthesized light beam is magnified and displayed on a screen (not shown) as a color image.
As described above, according to the projection display apparatus 1A that is the conventional example, a relatively simple optical structure can be achieved, and a high contrast color image can be obtained on a screen (not shown).
Next, a reflection type projection display apparatus 100A that is another conventional example illustrated in FIG. 2 is disclosed in the Patent Literature2 (U.S. Pat. No. 6,183,091B1 gazette) by Colorlink Inc.
The reflection type projection display apparatus 100A that is the conventional example is constituted of a light source portion 110 for emitting a white light beam; a color separation and color synthesis optical system 130A which color-separates the white light beam emitted from the light source portion 110 into three primary color light beams of R (red), G (green) and B (blue), guides these three primary color light beams to a spatial light modulators 120R, 120G and 120B corresponding to R (red), G(green) and B(blue) respectively, and emits a color-synthesized light beam obtained by color-synthesizing the three primary color light beams, which have been optically modulated by the spatial modulation elements 120R, 120G and 120B of the three primary colors in accordance with video signals; and a projection optical system 140 for projecting the color-synthesized light beam emitted from the color separation and color synthesis optical system 130A.
To be more specific, the foregoing light source portion 110 is constituted of a reflecting plane mirror 111; a light source 112 using a metal halide lamp, a xenon lamp, a halogen lamp or the like for emitting the white light beam; and a polarization plate 113 which is provided ahead of the light source 112 and has a transmission axis selected so as to transmit only an s-polarized light beam in the white light beam therethrough.
Accordingly, when the white light beam from the light source 112 transmits through the polarization plate 113, Rs, Gs and Bs light beams of an s-polarized light beam corresponding to R, G and B are incident onto the color separation and color synthesis optical system 130A provided between the light source portion 110 and the projection optical system 140.
The foregoing three spatial light modulators 120R, 120G and 120B use a reflection type liquid crystal panel and the like, and quarter wave plates 121 to 123 are integrally fitted to front planes of the three spatial light modulators (hereinafter, referred to as a reflection type liquid crystal panel) 120R, 120G and 120B. At this time, the quarter wave plates 121 to 123 serve to increase a contrast ratio of images of the respective colors displayed on the reflection type liquid crystal panels 120R, 120G and 120B.
The color separation and color synthesis optical system 130A surrounded by the dotted lines in FIG. 2 is constituted of one polarization beam splitter 131 formed to a rectangular parallelepiped shape (including a regular hexahedron shape); one dichroic prism 132 formed to a rectangular parallelepiped shape (including a regular hexahedron shape); one optical glass block 133 formed to a rectangular parallelepiped shape (including a regular hexahedron shape); and two, first and second, wavelength-selective polarization converting plates 134 and 135 formed to a plane shape. At this time, the outside dimensions of the polarization beam splitter 131, the dichroic prism 132 and the optical glass block 133 are set to be approximately equal in size.
Specifically, in the foregoing color separation and color synthesis optical system 130A, one polarization beam splitter 131 is located to face the left side plane thereof to the light source portion 110 and to face the lower side plane thereof to the projection optical system 140 when the light source portion 110 and polarization beam splitter 140 are in orthogonal position and one dichroic prism 132 is located so as to be adjacent to the upper side plane of the polarization beam splitter 131. Moreover, one optical glass block 133 is located so as to be adjacent to the right side plane of the polarization beam splitter 131.
In the course of forming of the above mentioned polarization beam splitter 131 in such a manner that two triangular prisms formed of optical glass showing no double refraction are jointed to form a rectangular parallelepiped shape, a semi-transmission reflection film which transmits a p-polarized light beam and reflects an s-polarized light beam is formed on one plane of one of the two triangular prisms, and another triangular prism is adhered onto the semi-transmission reflection film by use of light transmissivity adhesive, whereby a polarization separation plane 131a is formed along a diagonal by the semi-transmission reflection film.
In the course of forming the dichroic prism 132 in such a manner that two triangular prisms formed of optical glass showing no double refraction are jointed to form a rectangular parallelepiped shape, a semi-transmission film which transmits B color light beams (a Bs light beam and a Bp light beam) and reflects R color light beams (a Rs light beam and a Rp light beam) is formed on one plane of one of the two triangular prisms, and another triangular prism is adhered onto the semi-transmission reflection film by use of light transmissivity adhesive, whereby a dichroic half mirror plane 132a is formed along a diagonal by the semi-transmission reflection film.
The foregoing optical glass block 133 is formed to a rectangular parallelepiped shape by use of optical glass showing no double refraction.
The polarization beam splitter 131 and the dichroic prism 132 are located adjacently so that the polarization separation plane 131a of the polarization beam splitter 131 and the dichroic half mirror plane 132a of the dichroic prism 132 are approximately parallel when viewed from above.
On the right plane side of the dichroic prism 132, a reflection type liquid crystal panel 120R for R color, to which the quarter wave plate 121 is fitted, is placed so as to face thereto, and, on the upper plane side of the dichroic prism 132 a reflection type liquid crystal panel 120B for B color, to which the quarter wave plate 123 is fitted, is placed so as to face thereto. On the right plane side of the optical glass block 133, a reflection type liquid crystal panel 120G for G color, to which the quarter wave plate 22 is fitted, is placed so as to face thereto.
Accordingly, in the foregoing color separation and color synthesis optical system 130A, the polarization beam splitter 131 serves as a member on a light incident side/light emission side, and the dichroic prism 132 and the optical glass block 133 serve as members for separating incident light beams to be radiated onto the reflection type liquid crystal panels 120R, 120G and 120B and reflection light beams modulated by the reflection type liquid crystal panels 120R, 120G and 120B.
Still furthermore, a first wavelength-selective polarization converting plate (phase plate for G color) 134 having a function to rotate the plane of polarization of the G color light beam by 90 degrees is located between the light source portion 110 and the left side plane of the first polarization beam splitter 131. A second wavelength-selective polarization converting plate (phase plate for G color) 135 having a function to rotate the plane of polarization of the G color light beams by 90 degrees is also located between the lower side plane of the polarization beam splitter 131 and the projection optical system 140.
The foregoing projection optical system 140 is provided at the rear stage of the second wavelength-selective polarization converting plate (phase plate for the G color) 135 installed in the color separation and color synthesis optical system 130A. The projection optical system 140 is provided with a projection lens 141 to magnify and display a color image.
Herein, an operation of the projection display apparatus 100A having the above described structure, which is another conventional example, will be described.
The white light beam emitted from the light source 112 in the light source portion 110, which is an indefinite polarized white light beam, is first incident onto the polarization plate 113, and only the s-polarized light beam transmits through the polarization plate 113. Then, the Rs, Gs and Bs light beams of the s-polarized light beam, which correspond to the R, G and B colors respectively, are incident onto the wavelength-selective polarization converting plate (phase plate for G color) 134 in the color separation and color synthesis optical system 130A.
At this time, as described above, the wavelength-selective polarization converting plate 134 is the phase plate for the G color, which rotates the plane of polarization only for the G color light beam. Accordingly, when the Gs light beam of the s-polarized light beam transmits through the wavelength-selective polarization converting plate 134, the Gs light beam is polarized and converted to the Gp light beam of a p-polarized light beam. Since the wavelength-selective polarization converting plate (phase plate for G color) 134 does not act on the Rs and Bs light beams of the s-polarized light beam at all, the Rs and Bs light beams transmit intactly through the wavelength-selective polarization converting plate 134.
Then, the Gp light beam polarized and converted by the wavelength-selective polarization converting plate (phase plate for G color) 134 transmits through the polarization separation plane 131a of the polarization beam splitter 131, and travels straightly to be incident into the optical glass block 133. Thereafter, the Gp light beam is incident onto the reflection type liquid crystal panel 120G for the G color, which has the quarter wave plate 122 facing the right side plane of the optical glass block 133. The Gp light beam from the optical glass block 133 undergoes optical modulation depending on a video signal corresponding to the G color in the reflection type liquid crystal panel 120G for the G color, and becomes the Gs light beam of an s-polarized light beam component generated after being optically modulated. Thus, the Gs light beam is emitted from the reflection type liquid crystal panel 120G.
Furthermore, the Gs light beam from the reflection type liquid crystal panel 120G transmits through the optical glass block 133, and is reflected by the polarization separation plane 131a of the polarization beam splitter 131. Then, the Gs light beam is incident onto the second wavelength-selective polarization converting plate (phase plate for G color) 135 which is located on the lower plane side of the polarization beam splitter 131. Herein, as described above, since the second wavelength-selective polarization converting plate 135 is the phase plate for the G color, which rotates the plane of polarization of the G color light beam by 90 degrees, the Gs light beam of the s-polarized light beam is polarized and converted to a Gp light beam of a p-polarized light beam by the second wavelength-selective polarization converting plate 132, and emitted onto the projection optical system 140 side.
The Rs light beam of the s-polarized light beam, which has transmitted through the first wavelength-selective polarization converting plate (phase plate for G color) 134, is reflected by the polarized light beam plane 131a of the polarization beam splitter 131, and enters the dichroic prism 132 above the polarization beam splitter 131. Thereafter, the Rs light beam is reflected by the dichroic half mirror plane 132a of the dichroic prism 132, and incident onto the reflection type liquid crystal panel 120R for the R color, which has the quarter wave plate 121 facing the right plane side of the dichroic prism 132.
The Rs light beam from the dichroic prism 132 undergoes optical modulation depending on a video signal corresponding to the R color in the reflection type liquid crystal panel 120R for the R color, and becomes the Rp light beam of a p-polarized light beam component generated after being optically modulated. Thus, the Rp light beam is emitted from the reflection type liquid crystal panel 120R. Thereafter, the Rp light beam from the reflection type liquid crystal panel 120R is reflected by the dichroic half mirror plane 132a of the dichroic prism 132, and enters the polarization beam splitter 131 below the dichroic prism 132 again. Thereafter, the Rp light beam transmits through the polarization separation plane 131a of the polarization beam splitter 131, and is incident onto the second wavelength-selective polarization converting plate (phase plate for G color) 135 located on the lower plane side of the polarization beam splitter 131 straightly. Herein, as described above, since the second wavelength-selective polarization converting plate 135 is the phase plate for the G color, the second wavelength-selective polarization converting plate 135 does not act on the Rp light beams at all, and the Rp light beam is emitted into the projection optical system 140 side intactly.
The Bs light beam of the s-polarized light beam, which has transmitted through the first wavelength-selective polarization converting plate (phase plate for G color) 134, is reflected by the polarization separation plane 131a of the polarization beam splitter 131, and enters the dichroic prism 132 above the polarization beam splitter 131. Thereafter, the Rs light beam transmits through the dichroic half mirror plane 132a of the dichroic prism 132, and straightly enters the reflection type liquid crystal panel 120B for the B color, which has the quarter wave plate 123 facing the upper side plane of the dichroic prism 132.
The Bs light beam from the dichroic prism 132 undergoes optical modulation depending on a video signal corresponding to the B color in the reflection type liquid crystal panel 120B for the B color, and becomes the Bp light beam of a p-polarized light beam component generated after being optically modulated. Thus, the Bp light beam is emitted from the reflection type liquid crystal panel 120B. Thereafter, the Bp light beam from the reflection type liquid crystal panel 120B transmits through the dichroic half mirror plane 132a of the dichroic prism 132, and straightly enters the polarization beam splitter 131 below the dichroic prism 132 again. Thereafter, the Bp light beam transmits through the polarization separation plane 131a of the polarization beam splitter 131, and is straightly incident onto the second wavelength-selective polarization converting plate (phase plate for G color) 135 located on the lower plane side of the polarization beam splitter 131. Herein, as described above, since the second wavelength-selective polarization converting plate 135 is the phase plate for the G color, the second wavelength-selective polarization converting plate 135 does not act on the Bp light beams at all, and the Bp light beam is emitted into the projection optical system 140 side intactly.
Subsequently, the Rp, Gp and Bp light beams are emitted from the second wavelength-selective polarization converting plate 135 in a state where their planes of polarization are aligned with the p-polarized light beam, and thereafter a color-synthesized light beam obtained by color-synthesizing the Rp, Gp and Bp light beams is magnified and displayed on a screen (not shown) as a color image.
As described above, according to the projection display apparatus 100A that is another conventional example, a relatively simple optical structure can be achieved, and a high contrast color image can be obtained on a screen (not shown).
Incidentally, when the color separation and color synthesis optical systems 30A and 130A, which are the conventional examples respectively, are applied to the reflection type projection display apparatus 1A and 100A, a high contrast color image is obtained on a screen (not shown).
Herein, in order to obtain a color image with a higher image quality by adopting a part of a technical concept as to the color separation and color synthesis optical system 30A and 130A, which are the conventional examples, it is necessary to improve xe2x80x9ca resister deviationxe2x80x9d by adhering the wavelength-selective polarization converting plate provided by at least one in the color separation and color synthesis optical system 30A or 130A and the polarization beam splitter facing thereto, unlike the conventional example, and necessary to raise a lamp output of the light source 12 or 112 provided in the light source portion 10 or 110. However, when it is intended to obtain a brighter color image on a screen (not shown) by the above manner, there has been a problem that shading occurs for the projected color image.
At this time, when the cause of the foregoing shading is investigated, since optical energy is made stronger by the increase of the lamp output of the light source 12 or 112, temperature of an optical member, onto which a white light beam from the light source 12 or 112 in the color separation and color synthesis optical system 30A or 130A is incident, rises, and a difference of a thermal expansion between the at least one wavelength-selective polarization converting plate located one on a light beam incident side of the light source portion 10 or 110 and the polarization beam splitter adhered to the wavelength-selective polarization converting plate so as to face thereto is caused, and it was proved that shading for the projected color image occurs owing to the difference of the thermal expansion.
Moreover, when the wavelength-selective polarization converting plate is provided on a side for emitting the color-synthesized light beam obtained by color-synthesizing the colors from the reflection type liquid crystal panels for the R, G and B colors in the color separation and color synthesis optical system, a problem that the contrast ratio decreases due to the interface reflection light beam of the wavelength-selective polarization converting plate has occurred.
As to a color separation and color synthesis optical system applied to a reflection type projection apparatus, a color separation and color synthesis optical system has been desired, which is capable of suppressing shading which, in a color image projected on a screen, is caused due to a difference of a thermal expansion between a wavelength-selective polarization converting plate and a polarization beam splitter, and capable of suppressing a decrease in a contrast ratio occurred by an interface reflection light beam of a wavelength-selective polarization converting plate provided on a side from which a color-synthesized light beam is emitted. Accordingly, an object of the present invention is to provide such color separation and color synthesis optical system.
To achieve the foregoing object, there is provided a color separation and color synthesis optical system provided between a light source portion and a projection optical system in a reflection type projection display apparatus including the light source portion, a plurality of spatial light modulators and the projection optical system, the color separation and color synthesis optical system, including: a color separation optical system having a first polarization beam splitter for color-separating a white light beam emitted from the light source portion into a plurality of color light beams; a color synthesis optical system having a second polarization beam splitter for color-synthesizing the color light beams emitted from the plurality of spatial light modulators and emitting a color-synthesized light beam; and a wavelength-selective polarization converting plate which rotates a plane of polarization of a specific color light beam by 90 degrees, the wavelength-selective polarization converting plate being adhered to at least one of incidence and emission planes, onto/from which a light beam is incident/emitted, of at least one of the first and second polarization beam splitters, with a small gap by adhesive.
In a preferable embodiment of the present invention, an external periphery of the wavelength-selective polarization converting plate and an external periphery of the at least one of the incidence planes and the emission planes are adhered by speckles of adhesive.
In a preferable embodiment of the present invention, a reflection reduction coating is applied to a plane of the wavelength-selective polarization converting plate exposed to the air.
Furthermore, to achieve the foregoing object, there is provided a color separation and color synthesis optical system provided between a light source portion and a projection optical system in a reflection type projection display apparatus including the light source portion, a plurality of spatial light modulators and the projection optical system, the color separation and color synthesis optical system, including: a color separation optical system having a first polarization beam splitter for color-separating a white light beam emitted from the light source portion into a plurality of color light beams; a color synthesis optical system having a second polarization beam splitter for color-synthesizing the color light beams emitted from the plurality of spatial light modulators and emitting a color-synthesized light beam; a wavelength-selective polarization converting plate which rotates a plane of polarization of a specific color light beam by 90 degrees; and a frame which supports the wavelength-selective polarization converting plate, the frame being adhered to at least one of incidence and emission planes, onto/from which a light beam is incident/emitted, of at least one of the first and second polarization beam splitters by adhesive.
In a preferable embodiment of the present invention, an external periphery of the frame and an external periphery of the at least one of the incidence and emission planes are adhered by speckles of adhesive.
In a preferable embodiment of the present invention, a reflection reduction coating is applied to a plane of the wavelength-selective polarization converting plate exposed to the air.
To achieve the foregoing object, there is provided with a reflection type projection display apparatus including: a light source portion; a color separation optical system having a first polarization beam splitter for color-separating a white light beam emitted from the light source portion into a plurality of color light beams; a plurality of spatial light modulators for optically modulating the plurality of color light beams depending on video signals; a color synthesis optical system having a second polarization beam splitter for color-synthesizing the color light beams emitted from the plurality of spatial light modulators and emitting a color-synthesized light beam; a wavelength-selective polarization converting plate which rotates a plane of polarization of a specific color light beam by 90 degrees, the wavelength-selective polarization converting plate being adhered to at least one of incidence and emission planes, onto/from which a light beam is incident/emitted, of at least one of the first and second polarization beam splitters, with a small gap by adhesive; and a projection optical system for projecting the color-synthesized light beam emitted from the color synthesis optical system.
In a preferable embodiment of the present invention, an external periphery of the wavelength-selective polarization converting plate and an external periphery of the at least one of the incidence and emission planes are adhered by speckles of adhesive.
In a preferable embodiment of the present invention, a reflection reduction coating is applied to a plane of the wavelength-selective polarization converting plate exposed to the air.
Furthermore, to achieve the foregoing object, there is provided with a reflection type projection display apparatus including: a light source portion; a color separation optical system having a first polarization beam splitter for color-separating a white light beam emitted from the light source portion into a plurality of color light beams; a plurality of spatial light modulators for optically modulating the plurality of color light beams depending on video signals; a color synthesis optical system having a second polarization beam splitter for color-synthesizing the color light beams emitted from the plurality of spatial light modulators and emitting a color-synthesized light beam; a wavelength-selective polarization converting plate which rotates a plane of polarization of a specific color light beam by 90 degrees; a frame for supporting the wavelength-selective polarization converting plate; and a projection optical system for projecting the color-synthesized light beam emitted from the color synthesis optical system, wherein the frame is adhered to at least one of incidence and emission planes, onto/from which a light beam is incident/emitted, of at least one of the first and second polarization beam splitters by adhesive.
In a preferable embodiment of the present invention, an external periphery of the frame and an external periphery of the at least one of the incidence and emission planes are adhered by speckles of adhesive.
In a preferable embodiment of the present invention, a reflection reduction coating is applied to a plane of the wavelength-selective polarization converting plate exposed to the air.
The nature, principle and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.